KVM: vmx: speed up MSR bitmap merge

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The bulk of the MSR bitmap is either immutable, or can be copied from
the L1 bitmap.  By initializing it at VMXON time, and copying the mutable
parts one long at a time on vmentry (rather than one bit), about 4000
clock cycles (30%) can be saved on a nested VMLAUNCH/VMRESUME.

The resulting for loop only has four iterations, so it is cheap enough
to reinitialize the MSR write bitmaps on every iteration, and it makes
the code simpler.

Suggested-by: Jim Mattson <jmattson@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>

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Paolo Bonzini 2017-12-13 14:16:30 +01:00 • committed by Radim Krčmář

parent 1f6e5b2564

commit c992384bde

1 changed files with 42 additions and 36 deletions

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arch/x86/kvm/vmx.c

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